calibrate vs gradate

calibrate

verb
  • To mark the scale of a measuring instrument. 

  • To measure the caliber of a tube or gun. 

  • To check or adjust by comparison with a standard. 

gradate

verb
  • To bring to a certain strength or grade of concentration. 

  • To change imperceptibly from one gradation of tone etc. to another. 

  • To arrange in order of grades. 

How often have the words calibrate and gradate occurred in a corpus of books? (source: Google Ngram Viewer )